31 Kurosaki, Ken Kosuga, Atsuko Goto, Keita Muta, Hiroaki 2005 Tritt, T. Proceedings of the 24th International Conference on Thermoelectrics: ICT2005 Clemson, SC USA IEEE 308-311 June 2005 We have studied the thermoelectric properties Ag9TlTe5 and AgTlTe. The thallium compounds have extremely low thermal conductivities around 0.25 Wm-1K-1 from room temperature to about 700 K. The thallium compounds indicate very high ZT values; especially the highest ZT value of Ag9TlTe5 is 1.23 obtained at 700 K. Ag9TlTe5 is a unique material combining extremely low thermal conductivity and relatively low electrical resistivity.